<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body {
            background: #000;
            text-align: center
        }

        #c1 {
            background: #fff;
        }
    </style>

</head>

<body>
    <canvas id="c1" width="800" height="600">

    </canvas>
</body>
<script>
    let oC = document.getElementById('c1');
    let gd = oC.getContext('2d');       //图形上下文-绘图用的接口
    let l=50,t=50,w=100,h=100;
    //矩形
    gd.strokeRect(l,t,w,h)
    oC.onclick=function(ev){
        if(ev.offsetX>=l&&ev.offsetX<=l+w&&ev.offsetY>=t&&ev.offsetY<=t+h){
            alert('在')
        }else{
            alert('不在')
        }
    }



</script>

</html>